New or repaved roadway surfaces almost always require the application of roadway surface markings as a mechanism for visually providing motorists with lane demarcation lines for controlling and directing traffic. In the past, the process of applying new roadway surface markings consisted of first manually determining the center of the roadway surface and painting small dots to visually define the roadway center. A driver of a paint vehicle would then use the roadway center to guide a paint sprayer which would deposit paint along the path defined by the small dots.
Currently, this task is accomplished by determining the center of the roadway at a first location point by manually measuring the width of the roadway and placing a mark at the center point. This process is then repeated to determine the center point of the roadway at a second location point which is displaced from the first point. These two points now define the starting and ending points for a line segment which identifies the center path of the roadway. A chain or string line is then stretched between the first and second center points and small white (or other colored) painted dots are manually sprayed and spaced along the stretched chain giving a visual indication of the center line of the roadway. The chain or string line is then removed from the roadway surface. This entire process is then repeated for the next segment of the roadway using the ending position of the first segment as the starting position for the second segment. This process is continuously repeated until the location of the center of the entire roadway has been defined. The roadway center line is used as a reference to define the roadway mark path (i.e., the roadway center line defines the mark path).
Having defined the position of the center of the roadway, a truck equipped with line painting equipment is positioned over the white dots. The driver of the truck then uses the white dots as a visual guide along with a pointer for coarsely positioning the truck over the defined segments. A second operator sits at the rear of the truck and positions paint spray nozzles(s) mounted on a side moveable paint carriage directly over the dots for all defined segments of the roadway center. The side moveable carriage allows the second operator to apply the roadway marking paint at the desired location and to correct for any slight misalignment of the truck position with respect to the guide dots. The controlled paint spray nozzle array then applies the paint onto the roadway surface as the truck follows each center segment of the roadway. As the truck follows the mark path (i.e., the center of the roadway), the nozzle array applies the desired roadway mark (e.g., a single or multiple, solid or dashed, roadway marking) which may be offset from the mark path.
Although the current technology achieves the desired goal of providing a system for applying roadway markings, the current system is manually intensive and places the personal safety of workers at significant risk. For example, two workers are required to measure the starting and ending position of the segments, and two workers are required to actually paint the roadway markings (one worker is required to drive the truck and the other worker is required to operate both the carriage and paint dispensing equipment). In addition, to minimize the impact of applying the roadway surface markings to actively traveled roads and highways, the application of roadway markings is usually done in the late evening hours. During this time, traffic visibility is impeded and there is a significant potential for oncoming traffic to collide with those workers manually defining the starting and ending positions for each segment.
Previous attempts to automate the process of marking roadways included guiding the road marking equipment along a predetermined mark path using electromagnetic beams. Unfortunately, these methods required the placement of transmitters along the roadway. Other previous attempts have included the use of light beams arranged in a manner to define the proper path. Again, this attempt proved difficult to implement because of sunlight interference. Other attempts have included using radioactive marking material which would emit a characteristic fingerprint to define the roadway mark path. There are many disadvantages with using radioactive marking material, including health and safety issues, longevity (half-life) of the radioactive material, and disposal problems.
Other attempts to re-mark roadway surfaces have included using a drawing application program in combination with a global positioning system (GPS)-based paint sprayer. A drawing pattern is created using the drawing application program and geographical coordinates for the pattern which are manually defined and then used by the GPS paint sprayer to mark the roadway surface. This attempt requires that the drawing pattern for the roadway be predetermined and fails if the exact location of the roadway marking is inaccurately defined, or if the drawing pattern does not correspond exactly with the geographical position of the actual roadway.
U.S. Pat. Nos. 6,074,693 and 6,299,934 (related as a divisional) each disclose one example of a paint sprayer for marking roadways and fields with a drawing pattern. Both issued to Manning and titled “Global Positioning System Controlled Paint Sprayer,” the patents teach a system having an external computer and a GPS paint sprayer. The drawing pattern is created by a designer using either a geographical information system (GIS) which runs, or drawing application programs which run, on the external computer. A print file of the drawing pattern is created by the operating system software and is passed to the GPS paint sprayer. The print file may contain the geographical mapping of pixel data; instead, the geographical mapping of the pixel data may be completed within the GPS paint sprayer. In either case, the geographical mapping of the drawing pattern is determined and then stored in memory within the GPS paint sprayer. The GPS paint sprayer further includes a GPS receiver and a location comparator. The GPS receiver determines the geographical location of the GPS paint sprayer and the location comparator determines if a match occurs between the current GPS location of the paint sprayer and the geographical mapping of the drawing pattern. If a location match between the current GPS location of the GPS paint sprayer and geographical mapping data of the drawing pattern is detected, a control signal is sent to a spray nozzle which deposits paint or other material at the match location. Both lines and picture-like drawings can be marked onto a surface using this patented system.
The current roadway marking technology has at least several problems. One problem is that a significant amount of manual labor is required to accurately paint lines on roadways, and as a result workers are placed in an unsafe working environment during the roadway marking process. Another problem with current technology is the inability to easily and quickly obtain sampled geographical coordinates of the existing roadway line marks using GPS or GPS-based pseudolite arrays. A related problem is the inability to use this sampled data to generate a continuous function of the geographical coordinates for the entire mark path. Additional problems are the lack of an offsetting capability to determine other substantially parallel mark paths for line marking and, therefore, the inability to uniformly deposit paint or other material along the first (or second) mark path duplicating the previous mark.
Manning's '693 patent expressly notes certain disadvantages with the current roadway marking technology. Under the heading “Description of the Prior Art,” as column 1, lines 11-40, the '693 patent states: “Road markings are produced to a great extent with the assistance of so called ‘road marking’ machines which apply paint under pressure from spray nozzle jets onto the road surface. In marking the road it is quite important that the horizontal registration of the paint be accurate with respect to the position of the road. In the past even experienced machine operators have found it difficult to manually guide a road marking machine with sufficient accuracy even where old markings are available. Heretofore, attempts have been made to automatically detect the presence of old markings and to use their detection for automatically guiding the road marking machine and switching the spray nozzle on and off as required. However, such attempts have not been wholly satisfactory because a break in the old marking does not give steering guidance during breaks. Moreover, this approach is of no use whatsoever where the old marks have disappeared or for new markings. Various arrangements have been disclosed for solving these problems by automatically guiding the road marking machine along a pre-determined path using light or electromagnetic beams. However, these arrangements require transmitters to be placed along the road, and in the case of light beams, are degraded by the effect of sunlight. In order to overcome these problems, it has been proposed to embed material [that] emitting radiation in the path that is to be marked. However, this method suffers from the disadvantage that embedding the radiating material in the road surface can be costly. Furthermore, radiating materials tend to lose their effectiveness after a time period. Similar issues pertain to parking lots, air landing fields, and the like.”
Although Manning identifies certain disadvantages with the known roadway marking technology, the GPS-controlled paint spray system disclosed by Manning in the '693 and '934 patents has its own disadvantages. First, a designer must generate a drawing pattern and it must be assumed that the designer has accurately generated the drawing pattern. It must be further assumed that the actual constructed road matches the content of the drawing pattern. The system fails if a discrepancy exists between the actual and drawing pattern road position.
In addition, the disclosed system cannot maintain the accurate horizontal registration of the paint markings which is required when the drawing pattern does not accurately match the actual constructed roadway. This situation occurs where on-site construction changes are prompted by unforeseen construction problems. Such problems include, for example, bedrock formations, unstable ground structure, water runoff, and the like.
The designer using the system disclosed by Manning in the '693 and '934 patents must determine and enter data corresponding to the reference geographical location for the center of the drawing, scaling information, orientation information, and other aspect ratio information to accurately determine the marking size and orientation. Thus, the system may require registration, orientation, and size input. The designer also must enter data manually for road markings, such as end points for a line, or an equation using known geographical location coordinates. This includes known coordinates from a previous survey. The system assumes that the designer can accurately determine geographical mark locations.
For an arc, the designer must select the end points and a radius. Such selection does not allow for a smoothly constructed functional fit. The designer must manually join line segments used to make a relatively long continuous painted line. The track line, which is a line, is produced from individual points and is not a smoothly derived curve from a mathematically derived function.
The system disclosed by Manning relies on an available equation. It does not sample pre-existing roadway marks (or produce a set of spaced points). The system does not record cross track position relative to a GPS receiver. The '693 patent does not disclose any mechanism for producing a curved line. Finally, the system disclosed by Manning paints only when there is a location match between the current GPS-based location and one of the data points in the geographical mark location data.
Others have attempted to use a combination of video-grammetry (imagers) and navigation tools (GPS systems for example) to map roadway features including roadway marks. For example, a study of precise road feature localization using a mobile mapping system has been completed. To determine the location of a roadway mark, however, an operator must manually select the feature position (i.e., roadway mark) on the camera's u-v coordinates using a manual digitizing tool. The conventionally defined east, north, up (ENU) coordinates of the manually selected feature are then determined by the mobile mapping system.
This system is prone to positional inaccuracies of the operator and is not completely automated. Individual selection of each roadway mark is time consuming and dependent upon the skill and experience of the operator. Furthermore, no mechanism is provided to automatically inspect the roadway marks for reflectivity and contrast, length and width dimensions, mark fill percentage, and other important quality standards.
Additionally, vehicle-mounted roadway mark locators, inspection apparatus and marking systems which rely solely upon raw (i.e., not post-processed) GPS or GPS-based pseudolite array systems positional data are prone to many errors which may degrade the usefulness and accuracy of these systems.
For example, it is well known that functioning vehicle-mounted GPS or GPS-based pseudolite systems rely upon the continuous reception of ranging and other radio frequency signals by their respective GPS receiver(s). These signals are then decoded by the respective vehicle-mounted GPS receiver(s) to determine the geographical location of the vehicle and may then also be used to determine any point located on the vehicle (positional offset corrected).
However, if the reception of these signals are temporarily lost as the result of foliage obstructions, such as tree cover, or are lost as the result of the vehicle passing through a tunnel or other RF blocking obstruction, the GPS receiver fails to provide accurate geographical location data resulting in inaccurate roadway mark geographical location data.
Other sources of error exist and include the inherent random noise occurring during the reception of the GPS signals. Although real time kinematic (RTK) enhanced GPS-based systems improve the accuracy of the GPS or GPS-based pseudolite systems to centimeter accuracy, errors still arise particularly in determining the GPS geographical location of moving vehicles from raw GPS positional data even with the improvements afforded by RTK enhanced raw GPS-based systems. For example, RTK signal reception may be lost in addition to the GPS signals, thereby causing inaccurate geographical location data.
Moving vehicles are also prone to vibrations caused by pot holes and other roadway imperfections which may cause the GPS antenna to vibrate, yielding inaccurate determination of GPS geographical location data. Vehicle suspension systems may also cause vibrations as the vehicle moves along a roadway. Additionally, vehicle loads may change causing changes in the GPS antenna(s) location and therefore errors in determining the GPS location of the vehicle. For example, paint trucks carry large vessels of paint which is subsequently dispensed during the remarking process. The dispensing process decreases the vehicle load and may cause changes in the roll and pitch of the vehicle, again causing changes in the GPS antenna(s) location.
Therefore the loss of either RTK and GPS signals or both along with vehicle vibrations may cause geographical location inaccuracies for those roadway mark locators, inspection systems and markers singularly dependent upon the reception of only RTK and GPS signals. Thus there is a need in the roadway industry for locating, inspection and marking systems that requires less manual labor, increases the operational safety factor for workers, and is less expensive than the current roadway marking technology, and which will more accurately locate, inspect and uniformly mark roadway repaved surfaces.